The present invention relates to cells and populations thereof which can be used for treating CNS diseases.
Parkinson's disease is an age-related disorder characterized by progressive loss of dopamine producing neurons in the substantia nigra of the midbrain, which in turn leads to progressive loss of motor functions manifested through symptoms such as tremor, rigidity and ataxia.
Current treatment strategies for PD focus on restoring the depletion of dopamine, generally through the administration of the dopamine precursor L-DOPA (L-3-4-dihydroxyphenylalanine). L-DOPA, (the blood-brain barrier (BBB) penetrating precursor of dopamine), successfully increases the synthesis and release of dopamine. However, as the disease progresses, less dopaminergic neurons are available to synthesize dopamine from the precursor and the effectiveness of the treatment decreases whilst L-DOPA-induced dyskinesia appears. Other treatments with dopamine agonists, monoamine oxidants inhibitor or COMT inhibitors also demonstrate partial improvement but they cannot prevent progression of the disease.
Cell transplantation has been suggested as an alternative treatment option for repairing and replacing missing dopaminergic neurons. For such cell replacement therapy to work, implanted cells must survive and integrate, both functionally and structurally, within the damaged tissue.
The use of stem cells as a cellular source in cell replacement therapy for Parkinson's disease has been recently suggested. Stem cells have the ability to exist in vivo in an undifferentiated state and to self-renew. They are not restricted to cell types specific to the tissue of origin, and so they are able to differentiate in response to local environmental cues from other tissues. This capability of self renewal and differentiation has great therapeutic potential in curing diseases.
In Parkinson's disease the stem cell replacement strategy is based on the idea that restoration of dopamine (DA) neurotransmission is effected by cell grafts that integrate over time into the remaining tissue and produce a long-lasting functional tissue. There are two methods of treating stem cells for grafting in PD. In the first method, prior to transplantation, cells are differentiated in-vitro to dopaminergic neurons. This allows for standardization and quality-control of the relevant cells. The second method comprises transplantation of undifferentiated stem cells that are thought to differentiate in-vivo to dopaminergic neurons following implantation into the striatum or substantia nigra.
In theory, DA neurons for cell therapy in PD could be made from stem cells from four different sources: fetal dopaminergic neurons, neural stem cells, embryonic stem cells and bone marrow stem cells.
Bone marrow contains two major populations of stem cells: hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) occasionally referred to as bone marrow stromal cells.
Rat BMSC following differentiation were shown to express Tyrosine-hydroxylase (TH), choline acetyltransferase and beta-III tubulin [Woodbury, D., et al., J Neurosci Res. 69(6):908-17, 2002]. Clinical therapeutic potential of mouse BMSC in PD was demonstrated by injecting mouse BMSC intrastriatally to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. The transplanted cells survived and expressed TH. Moreover improvement on the rotarod test at 35 days following transplantation was indicated [Li, Y., et al., Neurosci Lett. 316(2):67-70, 2001].
U.S. Patent Appl. 20050265983 to the present inventors teach human dopamine synthesizing MSCs which expressed neuronal markers and transcription factors that characterize midbrain DA neuron following induction of neuronal differentiation.
As an alternative to a cell replacement strategy, where the grafted cells have to survive and possess morphological electrophysiological and functional dopaminergic properties, cell therapy may be aimed at restoring or reestablishing the normal anatomy (connectivity) and physiology (appropriate synaptic contacts and functioning) of the striatum.
Neurotrophic factors (NTFs) are secreted proteins that regulate the survival, functional maintenance and phenotypic development of neuronal cells. Alterations in NTF levels are involved in triggering programmed cell-death in neurons and thus contribute to the pathogenesis of Parkinson's and other neurodegenerative diseases.
One of the most potent NTF for dopaminergic neurons is called glial cell line-derived neurotrophic factor (GDNF). It is known to promote the survival of the dopaminergic neurons in the substantia nigra, promote neurite outgrowth, increase cell body size and also raise levels of TH. GDNF belongs to a family of proteins, related to the TGF-β-superfamily, currently consisting of four neurotrophic factors: GDNF, Neurturin (NTN), Persephin, and Artemin/Neublastin. These factors are known to serve as regulators of cell proliferation and differentiation.
An analysis of neural progenitor cells (ST14A) revealed that GDNF overproduction may be associated with up-regulation of genes involved in axonal sprouting, neurite outgrowth, spine formation, vesicle transport and synaptic plasticity [Pahnke J, et al, Exp Cell Res. 297(2):484-94, 2004]. It was also suggested that the neuroprotective activity of GDNF is via its activation of the antioxidant enzyme systems such as glutathione peroxidase, superoxide dismutase and catalase activities [Chao C C, Lee E H. Neuropharmacology, 38(6):913-6, 1999].
Various cells type produce GDNF including glia cells (oligodendrocytes and astrocyte), neuroblastoma and glioblastoma cell lines. It has recently been shown that rat BMSCs cultured in DMEM supplemented with 20% fetal bovine serum, at passage 6 express GDNF and NGF [Garcia R, et al., Biochem Biophys Res Commun. 316(3):753-4, 2004].
GDNF synthesis can be regulated by growth factors, hormones, cytokines and neurotransmitters. For example, tumor necrosis factor-α or interleukin-1 induces release of GDNF from glioblastoma cells. Forskolin or cAMP causes an increase in GDNF release by both the neuroblastoma and glioblastoma cell lines. These cells comprise neurotransmitter receptors, which allow the neurotransmitters to regulate growth factor production under conditions of stress.
Administration of GDNF directly into the brain has been shown to be effective in various animal models of PD. In addition, exposure of cells to GDNF prior to transplant has proven beneficial. For instance, grafting of 400,000 fetal dopaminergic neurons prior to transplantation significantly improved the rotational behavior of lesioned rats [Mehta V, et al., J. Neurosurg. 1999 April; 90(4):804-6].
Various methods have been used to aid administration of GDNF into the brain including osmotic pumps, capsules and microspheres. Another approach for GDNF delivery is in vivo gene therapy. Bone marrow mesenchymal cells genetically engineered to express GDNF, transplanted into MPTP-lesioned mice, were able to protect nigral neurons as well as striatal fibers [Park, K., Neurosci. Res. 40: 315-323, 2001].
Several studies have shown that MSCs following exposure to different factors in vitro, change their phenotype and demonstrate neuronal and glial markers [Kopen, G. C., et al., Proc Natl Acad USA. 96(19):10711-6, 1999; Sanchez-Ramos, et al. Exp Neurol. 164(2):247-56. 2000; Woodbury, D., J Neurosci Res. 61(4):364-70, 2000; Woodbury, D., et al., J Neurosci Res. 69(6):908-17, 2002; Black, I. B., Woodbury, D. Blood Cells Mol Dis. 27(3):632-6, 2001; Kohyama, J., et al. Differentiation. 68(4-5):235-44, 2001; Levy, Y. S. J Mol Neurosci. 21(2):121-32, 2003].
However, none of these studies have shown human MSCs capable of secreting significant levels of neurotrophic factors.
There is thus a widely recognized need for, and it would be highly advantageous to have, transplantable cells capable of synthesizing neurotrophic factors such as GDNF for the treatment of neurodegenerative disorders.